Summary

The effect of highly purified staphylococcal α-toxin on HEp-2 neoplastic cells growing in culture was studied by electron microscopy. In addition to some nuclear modifications, the most significant morphological changes were in mitochondrial structure. α-toxin seems to induce a defined sequence of changes in mitochondrial configuration which can be summarized as an earlier phase of ‘condensation’ of mitochondrial structure and a later phase of mitochondrial swelling with an intermediate ‘transitional’ configuration. The significance of these findings is discussed in the light of the present state of knowledge of the biological characteristics of staphylococcal α-toxin.